The present invention relates to an ignition apparatus for an internal combustion engine that prevents after burning.
A typical example of a known ignition apparatus for preventing after burning is illustrated in FIG. 3. The apparatus includes a signal generator 1 for generating a signal in synchronism with the rotation of an internal combustion engine, a waveform shaper 2 connected to the signal generator 1 for shaping the waveform of the output signal of the signal generator 1 into an appropriate form, a frequency to voltage (F/V) converter 3 connected to the waveform shaper 2 for converting the frequency of the thus shaped output signal of the signal generator 1 into a corresponding voltage, a reference voltage source 4 generating a reference voltage Vr corresponding to a predetermined number of revolutions per minute of the engine, a comparator 5 having a first positive or non-inverted input terminal connected to the F/V converter 3, a second negative or inverted input terminal connected to the reference voltage source 4 and an output terminal, and a synchronizer 6 connected to the waveform shaper 2 and the output terminal of the comparator 3. The synchronizer 6 comprises an AND gate 6a which has a first input terminal connected to the output terminal of the comparator 5 and a second input terminal connected through an inverter 6b to the waveform shaper 2, an AND gate 6c which has a first input terminal connected to a node between the inverter 6b and the second input terminal of the AND gate 6a and a second input terminal connected through an inverter 6d to a node between the output terminal of the comparator 5 and the first input terminal of the AND gate 6a, and a flip-flop circuit 6e having a set terminal connected to the output terminal of the first AND gate 6a and a reset terminal connected to the output terminal of the second AND gate 6c.
The apparatus further includes an AND gate 7 having a first input terminal connected to the waveform shaper 2, a second input terminal connected to the flip-flop circuit 6e of the synchronizer 6 and an output terminal, a driver 8 connected to the output terminal of the AND gate 7, a switch 9 in the form of a power transistor circuit connected to the driver 8, and an ignition coil comprising a primary winding and a secondary winding having their one end connected in common to a power source 11, the primary winding having the other end thereof connected to the power transistor circuit 9, and the secondary winding having the other end thereof connected to an unillustrated spark plug.
The operation of the known ignition apparatus as constructed above will now be described in detail with particular reference to waveform diagrams of FIGS. 4(a) and through 4(f).
First, the signal generator 1 generates an ignition signal A in synchronism with the rotation of the engine which has a waveform as shown in FIG. 4(a). The ignition signal A is input to the waveform shaper 2 which shapes the signal A to provide a shaped signal B having square pulses, as shown in FIG. 4(b). A part of the shaped signal B of the waveform shaper 2 is then fed to the F/V converter 3 where the frequency of the signal B is converted into a corresponding voltage C, as shown in FIG. 4(c), which in turn is supplied to the first input terminal of the comparator 5. The comparator 5 compares the output voltage C from the F/V converter 3 with the reference voltage Vr fed to the second input terminal thereof, and generates an output signal of a high level, as shown in FIG. 4(d), when the voltage C is greater than the reference voltage Vr.
The output signal D from the comparator 5 is input to the first input terminal of the AND gate 6a and at the same time to the second input terminal of the AND gate 6c through the inverter 6d. Based on the output signal B from the waveform shaper 2 and the output voltage D from the comparator 5, the synchronizer 6 generates a mask signal E, which has a waveform as shown in FIG. 4(e).
The mask signal E thus generated is fed to the second input terminal of the AND gate 7 to the first input terminal of which the output signal B from the waveform shaper 2 is input. When the signals B, E are both high, the AND gate 7 generates an output signal F in the form of an ignition control signal, as shown in FIG. 4(f), which is fed through the driver 8 to the power transistor circuit 9, making it conductive. With the conduction of the power transistor circuit 9, a current flows from the power source 11 into ground through the primary winding of the ignition coil 10 and the now conductive power transistor circuit 9, so that a high voltage is developed in the secondary winding, causing an unillustrated spark plug to generate a spark. Thus, as can be seen from FIGS. 4(c) and 4(f), when the number of revolutions per minute of the engine exceeds a predetermined value corresponding to the output voltage Vr of the reference voltage source 4, the known apparatus stops ignition, suppressing a further increase in the rotational speed of the engine.
The above-described known ignition apparatus, however, has the following problem. When the number of revolutions per minute of the engine, having once increased above the predetermined value, decreases again below the predetermined value due to continued non-ignition or misfiring of the spark plug for a prescribed period of time, ignition is restarted but at this time, after-burning phenomena will often take place due to resultant excessive fuel supply, abnormal combustion and the like.